Temperature and radioactive surveys while injecting steam to heat up viscous oil reservoirs have indicated that the steam tends to go into those zones previously treated. Cyclic steam stimulation becomes uneconomic when this occurs repeatedly. Also, the placement of steam in a steam drive in a thick productive section requires some sort of vertical zonal segregation to make the available thermal energy sufficiently concentrated to be effective. The use of packer cup assemblies is one way to achieve vertical zonal segregation. However, field evidence indicates that commercially available packer cup assemblies are not holding up under actual well conditions. Tests were made on many commercially available packer cup assemblies. Sealing elements of available packer cup assemblies were found to be not satisfactory. Further, available packer cup assemblies are not designed to permit easy washover as opposed to milling up if the assemblies become stuck in the hole.
Initially, it was thought that only a few psi pressure differential would be required to inject steam into a particular zone but this assumption was proven to be in error. A packer cup assembly was wanted which could be easily washed over or could be broken up and left in the bottom of the well. Most commercially available packer cups have a metal backup thimble which generally has an outside diameter 3/16 inch to 1/2 inch less than the inside diameter of the casing. Operators are reluctant to run multiple packer cup assemblies in a well where there is a history of sand production because the cups are often stuck by sand. The packer cup assemblies generally have to be cut and recovered singly or milled up because there is not wash-over clearance with the tight fitting metal backup thimbles. Therefore, there was need for a packer cup assembly which does not require metal backup thimbles or plates. If backup material is required it has to be made out of something that is frangible. Further, there is need for a packer cup assembly which will withstand reasonable pressure differential encountered at elevated temperatures and yet have the tubing string strong compared to the packer cup assembly so the tubing can be pulled from the well and the packer cup assembly dropped to the bottom of the well. Alternatively, it is desirable to be able to wash over the packer cup assembly with currently available wash pipe.